Graphene (G) is a two dimensional sheet of atomic carbon with very attractive physical, optical and mechanical properties, including high charge carrier mobility, record thermal conductivity and stiffness. Currently, upwardly scalable graphene synthesis methods mainly include a solution-based graphite oxide-mediated route and chemical vapor deposition (CVD).
Graphite oxide-derived methods of forming graphene produce graphene samples with poor crystalline quality and high defect density. Films prepared by such methods required a high-temperature annealing process to convert the graphene from an insulator to a conductor. The CVD method is suitable for preparing large-area thin films, but is not amenable to solution-based processing. Solution-based processing is needed for bulk processing of graphene composites, blends, inks, etc.
Conventional methods for the solution-based synthesis of graphene from direct exfoliation/intercalation have yields that are generally less than 10%. This means 90% of the starting material, which is graphite, remained unexfoliated, and only 10% or less of the starting material is recovered as graphene flakes, each comprising one or a few layers of graphene. A problem with such low-yield methods is that they require multiple steps to generate sufficient products for further processing, and include tedious multiple steps of separating the unexfoliated materials from the exfoliated material.
Thus, there is a need for a high-yield method of forming graphene flakes directly from graphite that bypasses oxidation treatment, i.e., without forming graphene-oxide (GO).